Carbon fibers are produced commercially from rayon, phenolics, polyacrylonitrile (PAN), or pitch. The latter type are further divided into fiber produced from isotropic pitch precursors, and those derived from pitch that has been pre-treated to introduce a high concentration of carbonaceous mesophase. High performance fibers, i.e. those with high strength or stiffness, are generally produced from PAN or mesophase pitches. Lower performance, general purpose fibers are produced from isotropic pitch precursors. These materials are produced as short, blown fibers (rather that continuous filaments) from precursors such as ethylene cracker tar, coal-tar pitch, and petroleum pitch prepared from decant oils produced by fluidized catalytic cracking. Applications of isotropic fibers include: friction materials; reinforcements for engineering plastics; electrically conductive fillers for polymers; filter media; paper and panels; hybrid yards; and as a reinforcement for concrete.
More recently, interest has developed in activated forms of isotropic carbon fibers, where high surface areas can be produced by partial gasification in steam or other oxidizing gases. Activated carbon fibers have novel properties that make them more attractive than conventional forms (powders or large-size carbons) for certain applications. While porosity can be generated in most types of carbon fiber, low modulus fibers produced from isotropic pitch are particularly suited for activation because of their unique structure, where the random packing of small crystallites allows the development of an extensive pore structure.
Among the possible applications, activated carbon fibers are of interest for the adsorption and recovery of organic vapors; in environmental protection; the removal of SO.sub.x and NO.sub.x from flue gas; the improvement of air quality; and water treatment. Difficulties in handling and utilizing activated carbon fibers can be surmounted by their incorporation into composites, such as woven and non-woven fabrics, felt and paper.